The proposed study examines psychological well-being and sibling relationships in adolescent siblings who have a brother or sister with an autism spectrum disorder (ASD). Prior studies on siblings of individuals with autism have examined sibling well-being from either a family stress perspective (that having a brother or sister with ASD is stressful to the family and thus causes negative outcomes) or a family genetics perspective (that traits associated with the "broader autism phenotype" are more prevalent in relatives of individuals with ASD due to genetic inheritance). The proposed study aims to unite these two approaches and examine their combined contribution to sibling well-being and the sibling relationship, using a stress-diathesis model. The four specific aims of the proposed research are: (1) to examine the extent to which the psychological well-being of adolescent siblings and the quality of the sibling relationship are associated with the presence of the "broader autism phenotype" in siblings (2) to examine the extent to which the psychological well-being of adolescent siblings and the quality of the sibling relationship are associated with environmental stressors (both familial and extra-familial), (3) to test a diathesis-stress model of sibling adaptation, examining the extent to which environmental stress characteristics of the broader autism phenotype interact to impact the sibling relationship and to determine sibling psychological well-being, and (4) to identify protective resources for adolescent siblings that may help moderate the impacts of environmental stresses and family genetic vulnerability to negative psychological outcomes. The proposed study builds directly on an ongoing study of 405 families of adolescents and adults with ASD, conducted by Dr. Marsha Seltzer and Dr. Marty Krauss (R01 AG08768-11-15). Adolescent siblings will be recruited from families already participating in that study, and will complete telephone interviews and mailed surveys. An overall goal of the study in this proposal is to establish a sample of siblings who, with additional funding in the future, could be followed longitudinally as they transition to adulthood.